1. Technical Field
The present invention relates generally to a disk drive system, and in particular to a method and apparatus for increasing effective storage capacity and read/write access speed by suppressing rotational tilt of hard disk drives.
2. Description of the Related Art
A hard disk drive (hereafter referred to as HDD) has a structure in which one or more magnetic disks are arranged on the same axis so as to be driven by a spindle motor. Data is read or written by a magnetic head provided so as to face the magnetic disk and the magnetic head is driven by an actuator, generally driven by a voice coil motor (hereafter referred to as VCM). The magnetic disk, magnetic head, and actuator are housed in a housing referred to as enclosure case.
Improving a storage capacity and read/write speed of a magnetic disk is a constant technological goal. In the case of the latter, it is possible to improve data read/write speed by shortening the seek time for a magnetic head to move to a necessary track on a magnetic disk. Because a magnetic head is driven by a VCM as described above, it is possible to increase a seek speed by improving the performance of the VCM. To improve the performance of a VCM, it is only necessary to change a permanent magnet constituting the VCM to one having a stronger magnetic characteristic or increase the thickness of the magnet to increase a magnetic field to be applied to a voice coil. However, improvement of the magnetic characteristic of a permanent magnet approaches a limit. Moreover, in the case of an HDD whose space must be decreased, there is a limit in further increasing the thickness of a permanent magnet from the current thickness.
It is possible to improve the data read/write speed by increasing the rotational speed of a magnetic disk. However, when increasing the rotational speed of a magnetic disk, the flutter of a magnetic head is increased. The flutter is a phenomenon in which a magnetic head is deflected in the radius direction of a magnetic disk due to the flow of air caused by rotation of the magnetic disk. When the flutter occurs, the relative positional relation between a magnetic disk and a magnetic head unnecessarily fluctuates and therefore, increase of the flutter value affects the data read/write accuracy. That is, data may be written in a track different from a track in which the data should be originally written or read from a track different from a track from which the data should be originally read. Particularly, by improving the storage density of a magnetic disk in order to increase the capacity of the disk, the above trend becomes more remarkable. For this problem, an art for attaching a damper to a magnetic-head slider is effective.
Furthermore, increasing the rotational speed of a magnetic disk results in increased power consumption. That is, when the rotational speed of a magnetic disk is increased, the windage loss to the rotation of the magnetic disk increases and thereby, the power consumed by a spindle motor for rotating the magnetic disk increases. For increase of power consumption due to increase of the rotation of a magnetic disk, it is effective to decrease the magnetic disk in diameter. By decreasing a magnetic disk in diameter, the storage capacity may be decreased. However, decrease of the storage capacity is almost prevented by the recent density-increase art.